U.S. patent number 7,116,480 [Application Number 10/075,657] was granted by the patent office on 2006-10-03 for method and apparatus for optical switching.
This patent grant is currently assigned to Oplink Communications, Inc.. Invention is credited to Wei-Zhong Li.
United States Patent |
7,116,480 |
Li |
October 3, 2006 |
Method and apparatus for optical switching
Abstract
An optical switch includes a first port, a second port, a first
component group, a second component group, and a switching
component group. The switching component group includes a
reflector, a polarization beam splitter coupled to the reflector,
and a polarization switch coupled to the polarization beam
splitter. The first component group is coupled between the first
port and the reflector in the switch component group. The second
component group is coupled between the second port and the
polarization beam splitter in the switch component group.
Inventors: |
Li; Wei-Zhong (San Jose,
CA) |
Assignee: |
Oplink Communications, Inc.
(San Jose, CA)
|
Family
ID: |
27732437 |
Appl.
No.: |
10/075,657 |
Filed: |
February 12, 2002 |
Current U.S.
Class: |
359/484.06;
359/489.11; 359/489.15; 359/489.07; 385/39; 398/57; 398/56 |
Current CPC
Class: |
G02B
27/283 (20130101); G02F 1/31 (20130101); G02B
6/3546 (20130101); G02B 6/3594 (20130101); G02F
1/09 (20130101) |
Current International
Class: |
G02B
5/30 (20060101) |
Field of
Search: |
;359/484,495-497,900
;385/11,22,27,33,47,36,39 ;349/196 ;398/55-57 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Robinson; Mark A.
Assistant Examiner: Fineman; Lee
Attorney, Agent or Firm: Fish & Richardson P.C.
Claims
What is claimed is:
1. A 2.times.2 optical switch comprising: a first port adapted to
receive an optical input and generate an optical output; a second
port adapted to receive an optical input and generate an optical
output; a switching component group including a singular
polarization switch; a first component group coupled between the
first port and the switching component group; a second component
group coupled between the second port and the switching component
group; wherein, when the singular polarization switch is disabled,
the switching component group being adapted to pass each light beam
exiting from the first component group, each exiting light beam
having a first chosen polarization, and reintroduce to the first
component group the light beams without changing the polarization
of the light beams, and to pass each light beam exiting from the
second component group, each exiting light beam having a second
chosen polarization, and reintroduce to the second component group
the light beams without changing the polarization of the light
beams, and when the singular polarization switch is enabled, the
switching component group being adapted to convert light beams
exiting from the first component group with the first chosen
polarization into light beams entering the second component group
with the second chosen polarization, and to convert light beams
exiting from the second component group with the second chosen
polarization into light beams entering the first component group
with the first chosen polarization.
2. The 2.times.2 optical switch of claim 1, wherein the first
component group is adapted to receive the optical input from the
first port and generate two light beams with the first chosen
polarization entering the switching component group, and to receive
two light beams with the first chosen polarization from the
switching component group and generate an optical output to the
first port; and the second component group is adapted to receive
the optical input from the second port and generate two light beams
with the second chosen polarization entering the switching
component group, and to receive two light beams with the second
chosen polarization from the switching component group and generate
an optical output to the second port.
3. The 2.times.2 optical switch of claim 1, wherein the singular
polarization switch includes a mirror.
4. The 2.times.2 optical switch of claim 1, wherein the singular
polarization switch includes a liquid crystal cell sandwiched
between two transparent conducting plates.
5. The 2.times.2 optical switch of claim 1, wherein the singular
polarization switch includes a Faraday rotator modulated by a
magnetic field.
6. The 2.times.2 optical switch of claim 1, wherein the first
component group comprises: a first birefringent material; a
structured half wavelength plate coupled to the first birefringent
material; a second birefringent material coupled to the structured
half wavelength plate; a half wavelength plate coupled to the
second birefringent material; and a Faraday rotator coupled to the
half wavelength plate.
7. The 2.times.2 optical switch of claim 1, wherein the first
component group comprises: a first birefringent material; a
structured half wavelength plate coupled to the first birefringent
material; a second birefringent material coupled to the structured
half wavelength plate; a Faraday rotator coupled to the second
birefringent material; and a half wavelength plate coupled to the
Faraday rotator.
8. The 2.times.2 optical switch of claim 1, wherein the switching
component group comprises, a reflector; a singular polarization
switch; and a polarization beam splitter coupled between the
reflector and the singular polarization switch.
9. An optical switch comprising: a first port adapted to receive an
optical input and generate an optical output; a second port adapted
to receive an optical input and generate an optical output; a
switching component group including: a reflector; a polarization
beam splitter coupled to the reflector; and a singular polarization
switch coupled to the polarization beam splitter; a first component
group coupled between the first port and the reflector in the
switching component group, the first component group operable to
provide light beams, each light beam having a first polarization,
to the switching component group; and a second component group
coupled between the second port and the polarization beam splitter
in the switching component group, the second component group
operable to provide light beams, each light beam having a second
polarization, to the switching component group.
10. The optical switch of claim 9, wherein the first component
group is adapted to receive the optical input from the first port
and generate one or more light beams with a first chosen
polarization entering the reflector in the switching component
group, and to receive one or more light beams with the first chosen
polarization from the reflector in the switching component group
and generate an optical output to the first port; and the second
component group is adapted to receive the optical input frorn the
second port and generate one or more light beams with a second
chosen polarization entering the polarization beam splitter in the
switching component group, and to receive one or more light beams
with the second chosen polarization from the polarization beam
splitter in the switching component group and generate an optical
output to the second port.
11. The optical switch of claim 9, wherein the singular
polarization switch includes a mirror.
12. The optical switch of claim 9, wherein the singular
polarization switch includes a liquid crystal cell sandwiched
between two transparent conducting plates.
13. The optical switch of claim 9, wherein the singular
polarization switch includes a Faraday rotator modulated by a
magnetic field.
14. The optical switch of claim 9, wherein the singular
polarization switch includes an optical filter.
15. The optical switch of claim 14, wherein the optical filter is a
tunable optical filter.
16. The optical switch of claim 9, wherein the first component
group comprises: a first birefringent material; a structured half
wavelength plate coupled to the first birefringent material; a
second birefringent material coupled to the structured half
wavelength plate; a half wavelength plate coupled to the second
birefringent material; and a Faraday rotator coupled to the half
wavelength plate.
17. The optical switch of claim 9, wherein the first component
group comprises: a first birefringent material; a structured half
wavelength plate coupled to the first birefringent material; a
second birefringent material coupled to the structured half
wavelength plate; a Faraday rotator coupled to the second
birefringent material; and a half wavelength plate coupled to the
Faraday rotator.
18. The optical switch of claim 9, wherein the second component
group comprises: a first birefringent material; a structured half
wavelength plate coupled to the first birefringent material; a
second birefringent material coupled to the structured half
wavelength plate; a half wavelength plate coupled to the second
birefringent material; and a Faraday rotator coupled to the half
wavelength plate.
19. The optical switch of claim 9, wherein the second component
group comprises: a first birefringent material; a structured half
wavelength plate coupled to the first birefringent material; a
second birefringent material coupled to the structured half
wavelength plate; a Faraday rotator coupled to the second
birefringent material; and a half wavelength plate coupled to the
Faraday rotator.
20. The optical switch of claim 9, where the polarization beam
splitter of the switching component group is coupled between the
reflector and the singular polarization switch.
21. The optical switch of claim 9, where the singular polarization
switch further comprises: a reflection mirror; a switch component
including a cell positioned between a fist and a second conducting
plate, the switch component operable to rotate a polarization of a
light beam when enabled and to pass a light beam without rotation
when disabled.
22. An optical switch comprising: a first port adapted to receive
an optical input and generate an optical output; a second port
adapted to receive an optical input and generate an optical output;
a switching component group including: a reflector; a polarization
beam splitter coupled to the reflector; and a singular polarization
switch coupled to the polarization beam splitter; a first component
group including: a first birefringent material coupled to the first
port; a structured half wavelength plate coupled to the first
birefringent material, the structured half wavelength plate being
operable to rotate a polarization of light passing through a first
portion of the structured half wavelength plate while the
polarization of light passing through a second portion of the
structured half wavelength plate remains substantially unchanged; a
second birefringent material coupled to the structured half
wavelength plate; and a polarization component subgroup including a
coupled half wavelength plate and a Faraday rotator, the
polarization component group coupled between the second
birefringent material and the reflector in the switching component
group; and a second component group including: a first birefringent
material coupled to the second port; a structured half wavelength
plate coupled to the first birefringent material; a second
birefringent material coupled to the structured half wavelength
plate; and a polarization component subgroup including a coupled
half wavelength plate and a Faraday rotator, the polarization
component group coupled between the second birefringent material
and the polarization beam splitter in the switching component
group.
23. An optical switch comprising: a first port adapted to receive
an optical input and generate an optical output; a second port
adapted to receive an optical input and generate an optical output;
a switching component group including: a reflector; a polarization
beam splitter coupled to the reflector; and a singular polarization
switch coupled to the polarization beam splitter; a first component
group coupled between the first port and the reflector in the
switching component group and including a non-symmetrical device,
the first component group adapted to provide an optical output
having a first polarization to the switching component group; and a
second component group coupled between the second port and the
polarization beam splitter in the switching component group and
including a non-symmetrical device, the second component group
adapted to provide a optical output having a second polarization to
the switching component group, wherein each of the non-symmetrical
devices allows for a traversal of light beams along different paths
in a respective component group when the light beams pass round
trip through the respective component groups.
24. The optical switch of claim 23, where the polarization beam
splitter of the switching component group is coupled between the
reflector and the singular polarization switch.
Description
The present invention relates generally to optical technology.
BACKGROUND OF THE INVENTION
A 2.times.2 optical switch is an optical component that provides
switching between two input ports and output ports. Optical signals
arriving at a given input port are transmitted to one of the output
ports depending on the state of the optical switch. The 2.times.2
optical switch can be configured in one of two possible states as
controlled by an external control signal. In a first state, an
optical signal received from a first input optical fiber at a first
input port is transmitted to a first output port that is in turn
coupled to a first output optical fiber. In addition, an optical
signal received from a second input optical fiber at the second
input port is transmitted to a second output port that is in turn
coupled to a second output optical fiber. In the second state, the
optical signal provided from first input optical fiber is
transmitted to the second output optical fiber, and the optical
signal provided from the second input optical fiber is transmitted
to the first output optical fiber. 2.times.2 optical switches are
widely used in communications equipment and are required to be
reliable, compact, and have robust performance across different
operating conditions.
SUMMARY OF THE INVENTION
In one aspect, the invention provides an optical switch. A first
port receives an optical input and generates an optical output. A
second port receives an optical input and generates an optical
output. A switching component group includes a polarization switch.
A first component group is coupled between the first port and the
switch component group. A second component group is coupled between
the second port and the switch component group. When the
polarization switch is disabled, the switch component group
converts two light beams exiting from the first component group
with a first chosen polarization into two light beams reentering
the first component group with the first chosen polarization, and
converts two light beams exiting from the second component group
with a second chosen polarization into two light beams reentering
the second component group with the second chosen polarization.
When the polarization switch is enabled, the switch component group
converts two light beams exiting from the first component group
with the first chosen polarization into two light beams reentering
the second component group with the second chosen polarization, and
converts two light beams exiting from the second component group
with the second chosen polarization into two light beams reentering
the first component group with the first chosen polarization.
In another aspect, the invention provides an optical switch. A
first port receives an optical input and generates an optical
output. A second port receives an optical input and generates an
optical output. A switching component group includes a reflector, a
polarization beam splitter coupled to the reflector, and a
polarization switch coupled to the polarization beam splitter. A
first component group is coupled between the first port and the
reflector in the switch component group. A second component group
is coupled between the second port and the polarization beam
splitter in the switch component group.
In another aspect, the invention provides an optical switch. A
first port receives an optical input and generates an optical
output. A second port receives an optical input and generates an
optical output. A switching component group includes a reflector, a
polarization beam splitter coupled to the reflector, and a
polarization switch coupled to the polarization beam splitter. A
first component group includes a first birefringent material
coupled to the first port, a structured half wavelength plate
coupled to the first birefringent material, a second birefringent
material coupled to the structured half wavelength plate, and a
polarization component subgroup. The polarization component
subgroup includes a half wavelength plate coupled to a Faraday
rotator. The polarization component group is coupled between the
second birefringent material and the reflector in the switching
component group. A second component group includes a first
birefringent material coupled to the second port, a structured half
wavelength plate coupled to the first birefringent material, a
second birefringent material coupled to the structured half
wavelength plate, and a polarization component subgroup. The
polarization component group includes a half wavelength plate
coupled to a Faraday rotator. The polarization component group is
coupled between the second birefringent material and the
polarization beam splitter in the switching component group.
In another aspect the invention provides an optical switch. A first
port receives an optical input and generates an optical output. A
second port receives an optical input and generates an optical
output. A switching component group includes a reflector, a
polarization beam splitter coupled to the reflector, and a
polarization switch coupled to the polarization beam splitter. A
first component group is coupled between the first port and the
reflector in the switch component group and includes a
non-symmetrical device. A second component group is coupled between
the second port and the polarization beam splitter in the switch
component group and includes a non-symmetrical device. Each of the
non-symmetrical devices allows for a traversal of light beams along
different paths in a respective component group when the light
beams pass round trip through the respective component groups.
In another aspect, the invention provides an optical component. The
optical component includes a first birefringent material, a first
structured half wavelength plate coupled to the first birefringent
material, a second birefringent material coupled to the first
structured half wavelength plate, a second half wavelength plate
coupled to the second birefringent material, and a Faraday rotator
coupled to the second half wavelength plate.
In another aspect, the invention provides an optical component
group. The optical component group includes a first birefringent
material, a structured half wavelength plate coupled to the first
birefringent material, a second birefringent material coupled to
the structured half wavelength plate, a Faraday rotator coupled to
the second birefringent material, and a half wavelength plate
coupled to the Faraday rotator.
Aspects of the invention can include one or more of the following
advantages. The present invention provides an easily manufacturable
2.times.2 optical switch with two optical ports such that an
optical signal introduced at one port can be returned to the same
optical port or the different optical port. Other advantages will
be readily apparent from the attached figures and the description
below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a 2.times.2 optical switch.
FIG. 2a illustrates the optical path through the switch of FIG. 1
for an optical input introduced at port 1 when the polarization
switch is disabled.
FIG. 2b illustrates the optical path through the switch of FIG. 1
for an optical input introduced at port 2 when the polarization
switch is disabled.
FIG. 3a illustrates the optical path through the switch of FIG. 1
for an optical input introduced at port 1 when the polarization
switch is enabled.
FIG. 3b illustrates the optical path through the switch of FIG. 1
for an optical input introduced at port 2 when the polarization
switch is enabled.
FIG. 4 shows one implementation of an optical switch including a
filter.
FIG. 5a and FIG. 5b show schematically the optical paths traversed
by light introduced at port 100 and port 200 of the optical switch
of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to an improvement in optical
technology. The following description is presented to enable one of
ordinary skill in the art to make and use the invention and is
provided in the context of a patent application and its
requirements. Various modifications to the invention will be
readily apparent to those skilled in the art and the generic
principles herein may be applied to other embodiments. Thus, the
present invention is not intended to be limited to the embodiments
shown, but is to be accorded the widest scope consistent with the
principles and features described herein.
The present invention will be described in terms of a 2.times.2
optical switch having specific components having a specific
configuration. Similarly, the present invention will be described
in terms of 2.times.2 optical switch components having specific
relationships, such as distances or angles between components.
However, one of ordinary skill in the art will readily recognize
that this method and system will operate effectively for other
components having similar properties, other configurations, and
other relationships between components.
Referring now to FIG. 1, a perspective view of one implementation
of a 2.times.2 optical switch 1000 is shown. The 2.times.2 optical
switch 1000 includes two ports, a port 100, and a port 200. The
port 100 is coupled to a first fiber (not shown) and is operable to
receive and transmit optical signals. The port 200 is coupled to a
second fiber (not shown) and is operable to receive and transmit
optical signals. The 2.times.2 optical switch 1000 is configured
for two possibilities as determined by a control signal applied to
the optical switch: (1) when the control signal is not present, an
optical signal received at one port (e.g., port 100) will be
transmitted back to the same port (e.g., port 100); and (2) when
the control signal is present, an optical signal received at one
port (e.g., port 100) will be transmitted to another port (e.g.,
port 200).
For ease of illustration, the components included in 2.times.2
optical switch 1000 are divided into three component groups:
component group 10 generally relates to port 100, component group
20 generally relates to port 200, and component group 30 generally
relates to components for switching between port 100 and port
200.
Component group 10 includes port 100, wedge 110, birefringent
material 120, phase compensation material 122, structured Half Wave
Plate ("HWP") 130, birefringent material 140, HWP 150, and Faraday
rotator 160. Port 100 further includes a collimator (not
shown).
Component group 20, is very similar to component group 10, and
includes port 200, wedge 210, birefringent material 220, phase
compensation material 222, structured HWP 230, birefringent
material 240, HWP 250, and Faraday rotator 260. Port 200 further
includes a collimator (not shown).
Component group 30 includes reflector 310, Polarization
BeamSplitter ("PBS") 320, and polarization switch 300. In one
implementation, polarization switch 300 includes a reflection
mirror 308 and a liquid crystal cell 305 sandwiched between
transparent conductor plates 301 and 302.
A light beam may enter one of four regions of a given component in
component group 10 or component group 20. The four regions are
labeled as quadrant I, II, III, IV, as shown in FIG. 1. The x and y
directions are also shown. The positive z direction is along the
propagation direction of a light beam introduced at ports 100 or
200.
FIGS. 2a and 2b illustrate, respectively, the optical path
traversed by an optical signal introduced at port 1 and at port 2
when the polarization switch is disabled. FIGS. 3a and 3b
illustrate, respectively, the optical path traversed by an optical
signal introduced at port 1 and at port 2 when the polarization
switch is enabled.
A. Component Group 10
Referring to FIG. 1, component group 10 performs two functions: (1)
an input light beam entering port 100 will be split into two light
beams with the x-polarization, and exit respectively from quadrants
I and II of Faraday rotator 160 in the positive z-direction; (2)
two light beams with the x-polarization, entering quadrants I and
II of Faraday rotator 160 in the negative z-direction, after
passing through component group 10, will be merged and exit from
port 100 as one output light beam.
Input light introduced at port 100 is generally deflected in the
y-direction by a collimator (not shown). The light beam, after
being deflected in the y-direction, is corrected by wedge 110 to be
traveling generally in the z-direction. The corrected beam enters
quadrant II of birefringent material 120. The polarization of light
beams before entering birefringent material 120 is represented by
symbol 112 in FIG. 2a.
An optical signal input to a port is typically randomly polarized.
The optical signal can be decomposed into two components with the
state of polarization (SOP) of each orthogonal to each other and to
the propagation direction. The two components are referred to as
"o" and "e" rays. Thus, an input optical signal can be decomposed
into a first portion having a first polarization and a second
portion having a second polarization. Birefringent material 120 is
a displacement element that is used to decompose light traveling in
a z-direction into first and second portions and to join two
portions having first and second polarizations when traveling in
the negative z-direction.
Birefringent material 120 is constructed and orientated in such a
way that a light beam traveling in the z-direction with the
y-polarization will pass through birefringent material 120
undeflected, while a light beam traveling in the z-direction with
the x-polarization will be deflected in the x-direction.
Accordingly, birefringent material 120 splits or joins light beams
in accordance with their respective polarizations as will be
discussed below. Light received on the input is assumed to be of
random polarization. A light beam with y-polarization received from
wedge 110, passes through birefringent material 120 and phase
compensation material 122, and enters quadrant II of structured HWP
130. A light beam with the x-polarization received from wedge 110,
is deflected in the x-direction by birefringent material 120, and
enters quadrant I of structured HWP 130. The polarization of light
beams before entering structured HWP 130 is represented by symbol
123 in FIG. 2a.
Structured HWP 130 is designed in such a way that the polarization
of a light beam passing through quadrants II or IV of structured
HWP 130 will be rotated by 90 degrees, and the polarization of a
light beam passing through quadrants I or III of structured HWP 130
will not change. The light beam with the x-polarization received
from quadrant I of birefringent material 120, passes through
structured HWP 130, and enters quadrant I of birefringent material
140 directly with the x-polarization. The light beam with the
y-polarization received from quadrant II of birefringent material
120, passes through structured HWP 130, and enters quadrant II of
birefringent material 140 with x-polarization. The polarization of
the light beams before entering birefringent material 140 is
represented by symbol 134 in FIG. 2a.
Birefringent material 140 is of similar construction to
birefringent material 120. Birefringent material 140 is a
displacement device constructed in such a way that a light beam
with the x-polarization passes through birefringent material 140
undeflected, and a light beam with the y-polarization passing
through material 140 is deflected. More specifically, a light beam
with the y-polarization traveling in the negative z-direction
passing through material 140 gets deflected in the negative
y-direction. The two light beams with the x-polarization received
from structured HWP 130, pass though birefringent material 140
un-deflected, and enter respectively quadrants I and II of HWP 150.
The polarization of the light beams before entering HWP 150 is
represented by symbol 145 in FIG. 2a.
HWP 150 is constructed in such a way that the polarization of a
light beam traveling in the z-direction will be rotated -45 degrees
with respect to the positive z-axis, and a light beam traveling in
the negative z-direction will be rotated +45 degrees with respect
to the positive z-axis. The two light beams received from
birefringent material 140, after passing through respectively
quadrants I and II of HWP 150, change from the x-polarization to
the x-y polarization, and enter respectively quadrant I and
quadrant II of Faraday rotator 160. The polarization of the light
beams before entering Faraday rotator 160 is represented by symbol
156 in FIG. 2a.
Faraday rotator 160 is constructed in such a way that the
polarization of a light beam traveling in the z-direction will be
rotated +45 degrees with respect to the positive z-axis, and a
light beam traveling in the negative z-direction will be rotated
+45 degrees with respect to the positive z-axis. The two light
beams received from HWP 150, after passing through respectively
quadrants I and II of Faraday rotator 160, change from the x-y
polarization to the x-polarization, and enter respectively
quadrants I and II of reflector 310. The polarization of the light
beams before entering reflector 310 is represented by symbol 167 in
FIG. 2a.
Light received at port 100, after passing through all components in
component group 10, is split into two light beams. The two light
beams exist respectively quadrants I and II of Faraday rotator
160.
HWP 150 is a reciprocal device. The polarization of a light beam
passing round trip (i.e., passing in the positive z-direction
through HWP 150, then reflected by a mirror, and passing back
through HWP 150 again in the negative z-direction) through HWP 150
is unchanged. Faraday rotator 160 is a non-reciprocal device. The
polarization of a light beam passing round trip (i.e., a light beam
passing in the positive z-direction through Faraday rotator 160,
then reflected by a mirror, and passing back through Faraday
rotator 160 again in the negative z-direction) through Faraday
rotator 160 is changed (e.g., rotated by a total of 90
degrees).
Because component group 10 includes a non-reciprocal device,
Faraday rotator 160, the two light beams exiting Faraday rotator
160 in the z-direction, when being reflected back into Faraday
rotator 160 by a mirror, follow optical paths in the negative
z-direction different from the optical paths traversed in the
z-direction. For example, the two light beams traveling in the
negative z-direction entering Faraday rotator 160 will eventually
be merged and exit port 110 as an output light beam, after passing
through all components in component group 10. More specifically,
two light beams with the x-polarization, after passing through
respectively quadrants I and II of Faraday rotator 160 in the
negative z-direction, become two light beams with the x+y
polarization. The polarization of the light beams before entering
Faraday rotator 160 is represented by symbol 176 in FIG. 2a. The
two light beams enter respectively quadrants I and II of HWP 150.
The polarization of light beams before entering the HWP 150 is
represented by symbol 165 in FIG. 2a.
The two light beams with the x+y polarization that pass through
respectively quadrants I and II of HWP 150 in the negative
z-direction, yield two light beams with the y-polarization. The two
light beams with the y-polarization enter respectively quadrants I
and II of birefringent material 140. The polarization of the light
beams before entering birefringent material 140 is represented by
symbol 154 in FIG. 2a.
The two light beams with y-polarization, traveling in the negative
z-direction, after passing through birefringent material 140, are
deflected in the negative y-direction, and enter respectively
quadrants III and IV of structured HWP 130. The polarization of the
light beams before entering structured HWP 130 is represented by
symbol 143 in FIG. 2a.
One light beam, after passing through quadrant III of structured
HWP 130, enters quadrant III of birefringent material 140 with
y-polarization. Another light beam, after passing through quadrant
IV of structured HWP 130, enters quadrant IV of birefringent
material 120 with x-polarization. The polarization of the light
beams before entering birefringent material 120 is represented by
symbol 132 in FIG. 2a.
The light beam with the y-polarization, after passing through phase
compensator 122, exits quadrant III of birefringent material 120
with y-polarization. The light beam with the x-polarization,
entering quadrant IV of birefringent material 120, is deflected in
the negative x-direction by birefringent material 120, and is
merged with light beams having the y-polarization in quadrant III
of birefringent material 120. The two beams merge at quadrant III
of birefringent material 120, are deflected together by wedge 110
(FIG. 1), enter one end of port 100 (FIG. 1), and exit from another
end of port 100 as an output light beam.
B. Component Group 20
Referring to FIG. 1, like component group 10, component group 20
also performs two functions: (1) an input light beam entering port
200 will be split into two light beams with the y-polarization, and
exit respectively in the z-direction from quadrants I and II of
Faraday rotator 260; (2) two light beams with the y-polarization,
entering quadrants I and II of Faraday rotator 260 in the negative
z-direction, after passing through component group 20, will be
merged and exit from port 200 as one output light beam.
With the exception of Faraday rotators 260 and 160, the function of
each component in component group 20 is similar to the function of
the corresponding component in component group 10. More
specifically, wedge 210 can be constructed similar to wedge 110,
birefringent material 220 similar to birefringent material 120,
phase compensation plate 222 similar to phase compensation plate
122, structured HWP 230 similar to structured HWP 130, birefringent
material 240 similar to birefringent material 140, and HWP 250
similar to HWP 150.
Because of these similarities, the path in component group 20
traversed by a light beam introduced at port 200 is similar to the
path in component group 10 traversed by a light beam introduced at
port 100.
Referring to FIG. 2b, an input light beam introduced at port 200 is
split into two light beams before entering Faraday rotator 260. The
two light beams exist respectively quadrants I and II of the HWP
250 in the positive z-direction with the x-y polarization, and
enter respectively quadrants I and II of Faraday rotator 260.
The polarization of the light beams in component group is
represented by symbol 212 before entering birefringent material
220, by symbol 223 before entering structured HWP 230, by symbol
234 before entering birefringent material 240, by symbol 245 before
entering HWP 250, and by symbol 256 before entering Faraday rotator
260.
Referring to FIG. 1, the Faraday rotators 260 and 160 differ in the
direction that the polarization of light changes (i.e., rotates)
when light passes through each. Faraday rotator 260 is constructed
in such a way that the polarization of a light beam traveling in
the positive z-direction will be rotated +45 degrees with respect
to the positive z-axis, and a light beam traveling in the negative
z-direction will be rotated +45 degrees with respect to the
positive z-axis. In contrast, Faraday rotator 160 is constructed in
such a way that the polarization of a light beam traveling in the
z-direction will be rotated -45 degrees with respect to the
positive z-axis, and a light beam traveling in the negative
z-direction will be rotated -45 degrees with respect to the
positive z-axis.
Referring to FIG. 2b, the polarizations of the two light beams
passing through respectively quadrants I and II of Faraday rotator
260 in the positive z-direction changes from the x-y polarization
to the y-polarization. The polarization of the light beams before
entering Faraday rotator 260 is represented by symbol 276 in FIG.
2b. After passing through Faraday rotator 260, the light beams with
y-polarization are incident upon respectively quadrants I and II of
polarization beam splitter 320.
When traveling in the reverse direction, the two light beams with
the y-polarization, from polarization beam splitter 320, enter
quadrants I and II of Faraday rotator 260 in the negative
z-direction. The two light beams with y-polarization, after passing
through respectively quadrants I and II of Faraday rotator 260 in
the negative z-direction, produce two light beams with x+y
polarization. The two light beams with the x+y polarization enter
respectively quadrants I and II of HWP 250. The polarization of the
light beams in component group 20 before entering HWP 250 is
represented by symbol 265 in FIG. 2b.
The two light beams entering respectively quadrants I and II of HWP
250 with x+y polarization, after passing though all the rest of the
components in component group 20, enter one end of port 200, and
exit from another end of port 200 as an output light beam.
Referring to FIG. 2b, the polarization of the light beams in
component group 20 is represented by symbol 254 before entering
birefringent material 240, by symbol 243 before entering HWP 230,
by symbol 232 before entering birefringent material 220, and by
symbol 221 before entering wedge 210.
C. Component Group 30
Referring to FIG. 1, component group 30 includes reflector 310,
Polarization BeamSplitter ("PBS") 320, and polarization switch
300.
Reflector 310 is constructed in such a way that a light beam
traveling in the z-direction will be reflected in the negative
y-direction, and a light beam traveling in y-direction will be
reflected in the negative z-direction.
PBS 320 is constructed in such a way that a light beam incident
upon PBS 320 with the x-polarization will be deflected, and a light
beam with the y-polarization will pass through PBS 320 without
deflection. More specifically, a light beam with the x-polarization
incident upon PBS 320 in the negative y-direction will be deflected
in the z-direction, and a light beam with the x-polarization and
incident upon PBS 320 in the negative z-direction will be deflected
in the y-direction. A light beam with the y-polarization incident
upon PBS 320 in either the positive or negative z-direction passes
through without deflection.
Polarization switch 300 includes reflection mirror 308 and liquid
crystal cell 305 sandwiched between transparent conductor plates
301 and 302. A bias voltage can be applied between the two
transparent conductor plates 301 and 302. In one implementation,
when a zero bias voltage is applied to the two conductor plates 301
and 302, polarization switch 300 is disabled. A light beam,
traveling in the z-direction, passes through conductor plate 301,
liquid crystal cell 305, and conductor plate 302, and maintains the
same polarization. The light beam, after being reflected by mirror
308, traveling in the negative z-direction, passes back through
conductor plate 302, liquid crystal cell 305, and conductor plate
301, and maintains the same polarization. Thus, when polarization
switch 300 is disabled, a light beam will maintain the same
polarization after being reflected by the polarization switch
300.
In one implementation, when a bias voltage Vb is applied to the two
conductor plates 301 and 302, polarization switch 300 is enabled. A
light beam, traveling in the z-direction, passes through conductor
plate 301, liquid crystal cell 305, and conductor plate 302. The
polarization of the light beam changes by 45 degrees. The light
beam, after being reflected by mirror 308, traveling in the
negative z-direction, passes back through conductor plate 302,
liquid crystal cell 305, and conductor plate 301. The polarization
of the light beam after reflection changes again by another 45
degrees. Thus, when polarization switch 300 is enabled, the
polarization switch 300 rotates the polarization of a light beam
reflected thereby a total of 90 degrees.
In one implementation, polarization switch 300 is constructed using
a liquid crystal cell. Alternatively, polarization switch 300 may
be constructed using a Faraday rotator controlled by a magnetic
filed. Other methods of constructing polarization switch 300 are
also possible.
Component group 30 supports four functions. When polarization
switch 300 is disabled, two light beams with the x-polarization,
exiting respectively from quadrants I and II of Faraday rotator
160, will be reflected and enter quadrants I and II of Faraday
rotator 160 in the negative z-direction with the x-polarization.
When polarization switch 300 is disabled, two light beams with
y-polarization, exiting respectively from quadrants I and II of
Faraday rotator 260, will be reflected and enter quadrants I and II
of Faraday rotator 260 in the negative z-direction with
y-polarization. When polarization switch 300 is enabled, two light
beams with the x-polarization, exiting respectively from quadrants
I and II of Faraday rotator 160, will be reflected and enter
quadrants I and II of Faraday rotator 260 in the negative
z-direction with y-polarization. Finally, when polarization switch
300 is enabled, two light beams with y-polarization, exiting
respectively from quadrants I and II of Faraday rotator 260, are
reflected and enter quadrants I and II of Faraday rotator 160 in
the negative z-direction with the x-polarization.
The first function of component group 30 is illustrated in FIG. 2a.
In FIG. 2a, polarization switch 300 is disabled. Two light beams
with the x-polarization, exiting respectively from quadrants I and
II of Faraday rotator 160, are reflected by reflector 310 to PBS
320. The two light beams incident upon PBS 320 with the
x-polarization are deflected in the z-direction and enter
polarization switch 300. Since polarization switch 300 is disabled,
the two light beams with the x-polarization are reflected back by
polarization switch 300 to PBS 320 with the same polarization.
These two light beams, traveling in the negative z-direction with
the x-polarization, are deflected by PBS 320 to reflector 310 in
the y-direction. After being reflected again by reflector 310, the
two light beams enter quadrants I and II of Faraday rotator 160 in
the negative z-direction with the x-polarization.
The second function of component group 30 is illustrated in FIG.
2b. In FIG. 2b, polarization switch 300 is disabled. Two light
beams with the y-polarization, exiting respectively from quadrants
I and II of Faraday rotator 260, are incident upon PBS 320. The two
light beams with the y-polarization pass through PBS 320, and enter
polarization switch 300. Since polarization switch 300 is disabled,
the two light beams with the y-polarization are reflected back by
polarization switch 300 to PBS 320 with the same polarization. The
two light beams traveling in the negative z-direction with the
y-polarization, pass through PBS 320, and enter quadrants I and II
of Faraday rotator 260 in the negative z-direction with the
y-polarization.
The third function of component group 30 is illustrated in FIG. 3a.
In FIG. 3a, polarization switch 300 is enabled. Two light beams
with the x-polarization, exiting respectively from quadrants I and
II of Faraday rotator 160, are reflected by reflector 310 to PBS
320. The two light beams incident upon PBS 320 with the
x-polarization are deflected in the z-direction and enter
polarization switch 300. Since polarization switch 300 is enabled,
the two light beams with the x-polarization are reflected back by
polarization switch 300 to PBS 320 with the y-polarization. The two
light beams traveling in the negative z-direction with
y-polarization, pass through PBS 320, and enter quadrants I and II
of Faraday rotator 260 in the negative z-direction with
y-polarization.
The fourth function of component group 30 is illustrated in FIG.
3b. In FIG. 3b, polarization switch 300 is enabled. Two light beams
with y-polarization (267), exiting respectively from quadrants I
and II of Faraday rotator 260, are incident upon PBS 320. The two
light beams with the y-polarization pass through PBS 320, and enter
polarization switch 300. Since polarization switch 300 is enabled,
the two light beams with the y-polarization are reflected back by
polarization switch 300 to PBS 320 with the x-polarization. The two
light beams, traveling in the negative z-direction with the
x-polarization, are deflected by PBS 320 to reflector 310 in the
y-direction. After being reflected again by reflector 310, the two
light beams enter quadrants I and II of Faraday rotator 160 in the
negative z-direction with the x-polarization (176).
A 2.times.2 optical switch can be constructed by combining three
the component groups 10, 20, and 30. In a first operational
scenario where polarization switch 300 is disabled, an input light
beam I1 entering port 100 will be returned as an output light beam
O1 from port 100, while an input light beam I2 entering port 200
will be returned as an output light beam 02 from port 200. In a
second operational scenario where the polarization switch 300 is
enabled, an input light beam I1 entering port 100 will be returned
as an output light beam O1 from port 200, while an input light beam
I2 entering port 200 will be returned as an output light beam O2
from port 100.
The 2.times.2 optical switch of FIG. 1 can be modified to add and
drop selected wavelengths in a given optical path. Referring now to
FIG. 4, the polarization switch 300 includes filter 306 placed in
front of conductor plate 301. Filter 306 can be constructed in such
a way that a light beam with wavelength .lamda. will be reflected,
and a light beam with wavelength .lamda.' will be transmitted. The
polarization switch 300 in FIG. 4 only switches the polarization of
a light beam with wavelength .lamda.'. When polarization switch 300
is disabled, a light beam with any wavelength will maintain the
same polarization after being reflected by the polarization switch
300. When polarization switch 300 is enabled, a light beam with
wavelength .lamda. will maintain the same polarization and a light
beam with wavelength .lamda.' will be rotated by 90 degrees, after
being reflected by the polarization switch 300.
FIGS. 5a and 5b show schematically the optical paths traversed by
light introduced at port 100 and port 200. As shown in FIG. 5a,
when polarization switch 300 is disabled, the light received at the
input I1 of port 100 with wavelengths .lamda. and .lamda.' are both
transmitted to the output O1 of port 100, and the light received at
the input I2 of port 200 with wavelengths .lamda. and .lamda.' are
both transmitted to the output O2 of port 200. As shown in FIG. 5b,
when polarization switch 300 is enabled, the light received at the
input I1 of port 100 with wavelength .lamda. is transmitted to the
output O1 of port 100 while the light received at port 100 with
wavelength .lamda.' is transmitted to the output O2 of port 200.
Similarly, the light received at the input I2 of port 200 with
wavelength .lamda. is transmitted to the output O2 of port 200
while the light received at the input I2 of port 200 with
wavelength .lamda.' is transmitted to the output O1 of port
100.
When polarization switch 300 of FIG. 4 is enabled, the light
received at the input I1 of port 100 with wavelength .lamda. is
transmitted to the output O1 of port 100. The light received at the
input I1 of port 100 with wavelength .lamda.' is dropped, and the
light received at the input I2 of port 200 with wavelength .lamda.'
is added and transmitted to the output O1 of port 100.
Filter 306 can be a tunable filter, such as a piezoelectric
controlled Fabry-Perot filter, and the wavelength being added and
dropped in the optical switch can be controlled by an external
variable. Filter 306 can also be constructed to transmit a number
of wavelengths or a band of wavelengths, and multiple wavelengths
can be added and dropped in the optical switch.
A method and system has been disclosed for providing a 2.times.2
optical switch, which may have low cost to manufacture. Although
the present invention has been described in accordance with the
embodiments shown, one of ordinary skill in the art will readily
recognize that there could be variations to the embodiments and
those variations would be within the spirit and scope of the
present invention. For example, the position of HWP 150 and Faraday
rotator 160 can be exchanged. The position of HWP 250 and Faraday
rotator 260 can be exchanged. Wedge 110 can be inserted between
birefringent material 120 and structured HWP 130. Wedge 210 can be
inserted between birefringent material 220 and structured HWP 230.
Wedge 110 and 210 can be replaced with half-wedges. The mirror 308
can be implemented to have certain wavelength selectivity, thus
enabling the 2.times.2 optical switch to switch optical signals
based on their respective optical wavelengths. Accordingly, many
modifications may be made by one of ordinary skill in the art
without departing from the spirit and scope of the appended
claims.
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